Our earlier studies have suggested that the reduced mitochondrial poly(A) polymerase activity in a series of Morris hepatomas is mostly due to inefficient endogenous or native primers present in their mitochondria. Since mitochondrial messenger RNA has been shown to contain a poly(A) sequence at the 3' terminus, it is conceivable that the endogenous primer is indeed the mitochondrial mRNA. In order to further explore the role of this native primer and to investigate other probable factors responsible for low poly(A) polymerase activity in the hepatoma mitochondria, the enzyme should be purified extensively. We have purified the enzyme from hepatoma 3924A to homogeneity. The capacity of the mitochondrial messenger RNA as the primer for this enzyme will now be investigated. The messenger RNA will be isolated by trapping it on poly(U)-impregnated filters or on poly(U) columns. These studies will answer the important question whether the primer closely associated with the enzyme preparations prior to purification is in fact the native messenger RNA. The properties of the primer from liver and tumor will be extensively investigated. The enzyme from a well differentiated (least deviated from liver) and undifferentiated (most deviated from liver) hepatoma will be solubilized and purified. Their properties will be compared with those from 3924A hepatoma, a poorly differentiated tumor. These studies will show any changes in enzyme characteristics induced by the degree of neoplastic growth. Concurrently, the primers will be isolated and their properties will be compared.